MTL - The Science Fiction World of Xueba-Chapter 378 Solicit

To clarify the mechanism of superconductors, physicists have proposed a variety of theories, including the London equation proposed in 1935 to describe the relationship between superconducting currents and weak magnetic fields, and the Pippard proposed in 1950 to 1953 to improve the London equation. Theory, the GL theory proposed in 1950 to describe the relationship between superconducting currents and strong magnetic fields (close to the critical magnetic field strength); the BCS theory proposed in 1957 to explain the first type of superconductors from a microscopic mechanism ... until now, Scientists have begun to propose a new mechanism for achieving superconductivity through quantum phase transitions: the topological defects of quantum spin Hall insulators condense to form superconductors.

In this case, the more important are GL theory and BCS theory.

GL theory is a phenomenological theory based on Landau's second-order phase transition theory.

The authors of the martingale theory were Gunzburg and Landau.

GL theory is proposed based on the following considerations: When the external magnetic field strength is close to the superconducting magnetic field strength, the current of the superconductor does not obey the linear law, and the zero-point vibration energy of the superconductor cannot be ignored.

The biggest contribution of GL theory is to foresee the existence of the second type of superconductor.

出发 From the GL theory, the concept of surface energy κ can be derived.

When the surface energy κ> 1 / √2 of a superconductor, it is a first type superconductor; when the surface energy κ <1 / √2 of a superconductor, it is a second type superconductor.

BCS theory is a theory based on the near-free electron model and the premise of weak electron-phonon interactions.

The authors of martingale theory are * ardeen, Cooper, and J.R. Schrieffer.

BCS theory believes that electrons with opposite spin and momentum in metal can be paired to form a Cooper pair, which can move without loss in the crystal lattice to form a superconducting current.

In short, we can compare the electron to a bee with only one wing. Such a bee cannot fly, but two such bees are combined, and the wings can be agitated one by one, and they can fly. Already.

For the cause of the Cooper pair, the BCS theory explains as follows: When the electrons move in the crystal lattice, they will attract positive charges on adjacent lattice points, causing local distortion of the lattice points, forming a local high positive charge region. This local region of high positive charge will attract electrons with opposite spins and pair with the original electrons with a certain binding energy. At very low temperatures, this binding energy may be higher than the energy of the lattice atom vibration, so that the electron pair will not exchange energy with the lattice, there is no resistance, and a superconducting current is formed.

BCS theory explained the reason for the existence of the first type of superconductor from the micro level. The authors of the theory, Buding, Cooper, and Schriver, won the 1972 Nobel Prize in Physics.

But the BCS theory cannot explain the reason for the existence of the second type of superconductor, especially the McMillan limit temperature (the critical transition temperature of the superconductor cannot be higher than 40K) based on the BCS theory.

Until now, the physics community has not formed a generally accepted superconducting formation mechanism.

As for the exploration of high temperature superconductors, a lot of progress has been made in academia.

In 1986, Mueller and Bernards discovered that a ceramic metal oxide, LaBaCuO4, consisting of barium, lanthanum, copper, and oxygen, has high-temperature superconductivity, with a critical temperature of 35K (﹣240.15 ° C).

陶瓷 Because ceramic metal oxides are usually insulating materials, this discovery is of great significance. Müller and Bernoz won the 1987 Nobel Prize in Physics.

Since then, research on high-temperature superconductivity has developed rapidly.

记录 With the promotion of scientists from China and the United States, this record has been continuously refreshed within five years.

In 1994, it set a new record of critical temperature of 135K at normal pressure and 164K at high pressure.

However, copper oxide high-temperature superconducting materials belong to oxide ceramics, lacking flexibility and ductility, and it is easy to lose superconductivity and heat quickly when carrying large currents. There are many technical difficulties in applying it.

Moreover, its physical properties and complexity are difficult to explain by existing theoretical frameworks.

By 2008, Japanese scientists discovered the existence of 26K superconductivity in the iron arsenide system. With the efforts of Chinese scientists, the critical temperature of such superconducting materials quickly exceeded 40K, and even reached 55K in bulk materials. Superconductivity.

So the new generation of superconducting family iron-based superconductors announced the discovery.

Rhenium is just that most of these superconductors contain arsenic or alkali metals and are sensitive to air. There are also many limitations in application.

As for the existence of room temperature superconductors, it is generally believed that they exist. Japanese scientists will even find superconductors above 400K as their long-term goal.

But it is not easy to confirm 100% the existence of a room temperature superconductor.

After all, to determine whether a new material is a superconductor, it must have both the characteristics of zero resistance effect and complete diamagnetism. If the resistance does not drop to zero or the diamagnetism is poor, it cannot be 100% determined to be superconducting.

In history, many "superconductors" have been dubbed by scientists as suspicious superconductors, referred to as USO, for lack of conclusive evidence.

这些 Among these USOs, some claim that they have superconductivity up to 200K or even 400K, but have never been proven by more experiments.

Some even resort to academic fraud for personal gain.

For example, a German named Jan Hendrik Sean once poured water in a frenzy in 2001, claiming to have found high-temperature superconductivity above 52K and other series of electronic device applications in C60 and other materials, and his thesis output Efficiency reaches the rate of one article every eight days.

In the end, physicists found that almost all of his thesis was falsified by data.

Sce series magazines retracted seven papers in 2002, Nature series magazines retracted eight papers in 2003, and dozens of other academic journals also retracted.

Later, his alma mater could not stand it and revoked his Ph.D. This scandal caused a sensation throughout the academic world. Sean was also known as a big liar in physics for 50 years.

Nevertheless, the academic community's enthusiasm for room temperature superconductors has not diminished.

Especially in recent years, new superconductors have been discovered almost every month.

比较 The most important one is that in 2015, German scientist A.P. Drozdov discovered that hydrogen sulfide has 203K superconductivity at 2 million atmospheres, but such harsh conditions can only be completed in the laboratory.

2019 By 2019, the A.P. Drozdov team confirmed that when the pressure was 1 million Earth atmospheric pressures, various hydrogen-rich lanthanide metal hydrides became superconductors at 250K, about -20 degrees below zero.

It can be said that at the laboratory level, it is only one step away from room temperature superconductors in the true sense.

Another important finding is related to the Chinese.

In 2018, MIT Jarillo Herrero's team found in experiments that double-layer graphene showed superconductivity at a twist angle of 1.1 degrees and a temperature of 1.7K.

的 The first author of this thesis is a Ph.D. student at MIT. A genius boy born in China, Cao Yuan, born in 1996. With this discovery, he topped the list of the top ten scientific figures in the world that were published by Nature in 2018.

The critical temperature of double-layer graphene superconductivity is very low, only 1.7K, which is basically of no practical value.

发现 This discovery is important because it presents a completely new physical phenomenon, which is completely different from other superconducting materials, which is of great significance for the interpretation of superconducting principles and finding high-temperature superconducting materials.

It took almost a week for Pang Xuelin to sort out the current state of research on superconductors in the real world, and concluded that the symmetry breaking of electromagnetic interactions will inevitably lead to changes in the movement of the electron clusters, thus triggering the superconducting phenomenon.

This is a definition of superconductivity in the practical field, and it is also the only consensus in academia on superconductors.

As for the theoretical explanation, then the Eight Immortals have their magical powers across the sea.

Uh ...

Combing the current research status of superconducting materials is only the first step of Pang Xuelin. Next, Pang Xuelin will have to study all the relevant technical papers brought back from the rural teacher world and the dark forest world.

In the world of rural teachers, Pang Xuelin obtained the quantum computer technology from the Carbon-based Life Alliance; in the dark forest world, he obtained a complete set of information on electromagnetic orbital propulsion technology and aerospace aircraft technology.

Pang Xuelin had not had time to study carefully before. Therefore, he needed to retreat for a period of time, after all these technologies were digested and absorbed, in order to really begin the deployment of electromagnetic orbital propulsion technology and the research and development of spacecraft technology.

Moreover, Pang Xuelin has 80% confidence to obtain relevant clues about room temperature superconductors from these materials.

As soon as Pang Xuelin arrived at the office that morning, he said to Zuo Yiqiu, "Xiao Zuo, help me see the schedule for the next week."

"Professor Pang, on October 12, that is, tomorrow morning, you will be attending the inauguration ceremony of the first Golden Dragon Battery Factory of the Golden Dragon Group. The Tianjiang Da Pang Xuelin Mathematical Center is officially unveiled. You must also participate. From October 15 to 20, it is Qiantang. The lab and the Jiangcheng Institute of Advanced Research will focus on interview time. At that time, more than one hundred scholars from all over the world will meet with you ... "

Pang Xuelin pondered for a moment and looked up: "When is the Nobel Prize Ceremony?"

"December 10."

Pang Xuelin said: "Help me to vacate the period from October 21 to December 8. This time, I will retreat, and do not let anyone disturb me."

"Retreat?"

I left Zuo Yiqiu for a moment, a little puzzled.

Pang Xuelin said: "I don't want to be disturbed when I conduct research."

"Oh."

Qi Zuo Yiqiu's face was astonished, and then Zuo Yiqiu said, "Yes, Professor Pang, the Dr. Cao Yuan whom you contacted me last week. He arrived in Jiangcheng in the afternoon to meet you.

"Cao Yuan arrives this afternoon?"

Xun Pang Xuelin's face showed surprise.

He asked Cao Yuan for research on superconductivity.

If there is a genius in this world, then Cao Yuan is undoubtedly one of them.

Even to a certain extent, Cao Yuan is a real genius compared to Pang Xuelin before the genetic optimizer transformation.

Cao Yuan is a native of Xichuan Province and has demonstrated his extraordinary talent for learning since childhood.

Because of his unique talents, he was favored by an experimental middle school in Shencheng at the age of eleven.

In Experimental Middle School, he completed all the courses in elementary and middle school in only three years.

Twenty-three years later, fourteen-year-old Cao Yuan was admitted to the Juvenile Class of the University of Science and Technology of China with a score of 668.

At the undergraduate level, Cao Yuan still achieved excellent grades and won the Guo Moruo Scholarship of the University of Science and Technology of China.

Twenty-eight years old, Cao Yuan graduated with an undergraduate degree and received an offer from MIT.

After entering MIT, Cao Yuan accidentally entered the Department of Electrical Engineering of MIT, although he missed the physics department he wanted to enter. He read a blog with her instructor Herrero, and then researched the related characteristics of double-layer graphene under HERRERO.

At the age of 22, Cao Yuan published two articles on graphene superconductivity in the journal Nature as the first author, which aroused widespread concern in the academic community.

In the same year, Cao Yuan made the unknown of the top ten scientific figures in the world that affected Nature in 2018.

Cao Yuan's later experience Pang Xuelin didn't know much. During this time, when he checked the superconducting data, he felt that Cao Yuan's discovery was very important for him to find a universal superconducting theory.

Therefore, he asked someone about the situation of Cao Yuan, and then he knew that Cao Yuan was already an associate professor of the University of Science and Technology of China. He independently led a team to conduct research on condensed matter physics.

So Pang Xuelin simply contacted Zuo Yiqiu with Cao Yuan, hoping to meet him.

He didn't expect Cao Yuan to rush over.

两 At 2:30 in the afternoon, Pang Xuelin met the talented boy who was only two years older than himself in the office.

Cao Yuan is a medium-sized man with a thin figure and wearing glasses. He looks very energetic.

The two were of the same age, and they were both new forces in the academic world, and they soon became acquainted.

After a short while, Han Han smiled, "Professor Cao, the reason I invited you over this time is to ask you, are you interested in joining Qiantang Lab?"

"Join Qiantang Lab?"

Cao Yuan froze slightly, and could not help but show a look of embarrassment on his face.

所以 The reason why he took the initiative to rush to Jiangcheng after receiving a call from Zuo Yiqiu was mainly interested in Pang Xuelin's team's large-sized and high-purity single-layer graphene preparation technology.

He has only returned to China for more than a year. Currently, he leads a team at the University of Science and Technology of China to conduct research on graphene superconductivity. There is no small gap in graphene at the Nanomaterials Research Center.

He also expected to get back some high-purity single-layer graphene from Pang Xuelin, but he did not expect that Pang Xuelin had the idea of ​​digging.

When I came to work in Qiantang Laboratory, this temptation was not small.

Especially after Kirton Walker and Pang Xuelin collaborated to get a lithium-air battery, people in academic circles who want to cooperate with Pang Xuelin are like Jiang Zhiyi.

Before Cao Yuan returned to China, Pang Xuelin gave him an olive branch, maybe he agreed on the spot.

But now he has just returned to the University of Science and Technology of China for more than a year. The welfare and scientific research conditions given to him by the University of Science and Technology are very good, and he was cultivated by the University of Science and Technology of China. He has a lot of affection for his alma mater. Some hesitation.

Pang Xuelin saw Cao Yuan's mentality at first glance and smiled, "Professor Cao, I don't mean to let you leave from the University of Science and Technology of China, but our Qiantang Laboratory and the University of Science and Technology of China work together to help you build a laboratory. Of course, you also It is a member of our Qiantang laboratory. My only requirement is that you can help me find possible superconductors in the field of carbon nanomaterials according to the relevant theoretical analysis I gave. "

"what?"

Cao Yuan slightly nodded, and nodded quickly: "Of course, no problem! I will ask the school leaders to mention it immediately after I return. I think our school will be very interested in cooperating with Qiantang Lab."

"That's good!"

Xi Pang Xuelin laughed.

According to his knowledge, Cao Yuan joined Pablo Jarillo-Herrero's team at MIT in 2014, and the team had already started trying to stack and rotate the carbon layers at different angles.

Cao Yuan's main work was to examine what would happen if one of the stacked double-layer graphenes was rotated by a very small angle relative to the other.

扭曲 According to a theoretical prediction, this distortion will greatly change the behavior of graphene, but many physicists are skeptical.

Cao Yuanyuan was determined to create this kind of double-layer graphene twisted at a subtle angle and discovered some strange phenomena.

Applying a weak electric field to graphene and cooling it to 1.7 degrees above absolute zero will make conductive graphene an insulator.

Then just adjust the electric field slightly, the twisted double-layer graphene can become a superconductor, allowing electrons to flow with zero resistance ~ www.novelbuddy.com ~ According to the situation learned by Pang Xuelin, Cao Yuan used the original in this experiment. The method first tears a single layer of graphene to form a double-layer graphene in the same direction, and then fine-tunes and calibrates based on this.

In addition, he also adjusted the low temperature system to reach a temperature that can make the superconducting state more significant.

In fact, at the time in the condensed matter physics community, a team also noticed that when the corner was about 1.2, the saddle point of the double-layer graphene system would drop to near the Fermi surface, and the tightly bound results were obviously different from the experimental results, which also meant that the system was strong Associated.

But no one thought of cooling down the system and doing transportation.

It can be seen that Cao Yuan's job was not derived from luck, but due to strength. They did very detailed experiments and were very clear about their expectations.

And Cao Yuan's strong hands-on ability has become the key to this achievement.

This is also the main reason he was able to be the author of those two papers.

Such a talented experimental physicist is the cooperation partner Pang Xuelin needs.

Next, Pang Xuelin and Cao Yuan talked about superconductivity issues and reached an agreement to help him expand the laboratory equipment and related teams. That evening, Pang Xuelin also specifically left Zuo Yiqiu to book a hotel for Cao Yuan. The conversation was very enjoyable.

As for the subsequent contacts with the University of Science and Technology and specific cooperation content, Pang Xuelin left it to his team to handle it.

After attending the inauguration ceremony of the first Jinlong Battery Factory and the unveiling of the Pang Xuelin Mathematical Research Center, Pang Xuelin spent another five days interviewing more than 100 scholars who wished to join the Qiantang Laboratory and Jiangcheng Advanced Institute, and then began to enter a closed state. .